Insulating sound: reducing how far it travels
Physics · Key Stage 2 · The School
Soft materials soak up sound
A hard, flat surface like a bare wall or a tiled floor reflects sound well, so a bare room sounds loud and echoey. A soft, uneven surface like a thick curtain, a carpet or a padded wall absorbs much of that sound instead of bouncing it back, so a furnished room sounds quieter and less echoey.
Why absorbing works
Sound is a vibration travelling through the air. A soft material is full of tiny gaps and fibres. Sound hitting it makes those fibres vibrate slightly and lose a little energy as heat, instead of bouncing the vibration straight back into the room. A hard surface has almost no give, so nearly all the sound bounces off it.
Where this matters in real life
A recording studio lines its walls with thick foam panels, full of gaps and bumps, to stop sound bouncing around and blurring a recording. A cinema uses heavy curtains and carpeted floors for the same reason. Even a simple room with a rug and curtains sounds noticeably calmer than the same bare room.
A small cardboard box with a ticking clock inside is tested twice. First, empty apart from the clock: the tick is clearly audible with the lid shut, because the hard cardboard reflects the sound out through any gap. Then the inside is lined with foam and cloth: the same clock, same box, but the tick is now much fainter. Nothing about the clock changed. Only the material lining the inside did — and that alone was enough to soak up most of the sound before it could escape.